The paint contained in the conventional paint container is drawn out by siphonage into a paint gun. In order to effect the siphonage, a considerable air current pressure is called for at the expense of the mechanical power. In light of the presence of excessive air current pressure, the paint is prone to be shot out by the paint spray gun in an excessive amount to result in the waste of the paint as well as the pollution of air by the paint spray. In addition, the coating so formed is often uneven in thickness.